1. Field of the Invention
The present invention relates to purification of gases containing harmful substances produced in manufacturing processes, transportation, combustion, waste disposal and the like in the industrial and consumer fields and, particularly, to a gas-purifying apparatus of purifying a gas discharged from garbage disposal, a purification catalyst for use therein and a preparation process therefor.
2. Description of the Related Art
In the gas purification technology gas purification methods of the adsortion type, ozone oxidation type, oxidative decomposition (combustion) type, biodegradation type and the like have been developed and improved in recent years. Among these methods, the method of the oxidative decomposition type using a catalyst has an advantage that it allows a garbage disposal apparatus which continually produces bad smell, to be rendered compact and maintenance-free and, hence, a gas-purifying apparatus employing this method has been put to practical use. Generally, activated alumina (Al2O3) carrying Pt or Pd is used as such a purification catalyst in combination with heating means such as a heater.
However, such a conventional gas-purifying apparatus employing the aforementioned catalytic oxidation method cannot sufficiently exhibit its ability under low temperature conditions at about 250° C. or below.
Garbage disposal apparatuses of the heat-drying type, bio-treatment type using microorganism and a like type that have been developed in recent years raise a problem that a gas produced therefrom gives off a bad smell. For this reason, the development of a gas-purifying apparatus having a higher gas-purifying ability at lower temperatures has been demanded.
Such a bad smell produced from a garbage disposal apparatus mainly comprises an organic sulfur compound, ammonia or an amine, a fatty acid such as acetic acid, propionic acid or valeric acid, and a combustible compound such as aldehyde or alcohol. One of the causes of a bad smell given off from a conventional garbage disposal apparatus is that a catalyst used cannot exhibit its catalytic performance sufficiently due to coexistence of various such smell components and moisture produced from garbage.
Among such smell components produced during garbage disposal, such compounds as methyl sulfide and methyl disulfide are hard to decompose at low temperatures in particular unlike hydrogen sulfide or the like. These sulfur oxides have raised a problem that they are easy to remain at a catalyst and act as poisoning substances with respect to the catalyst. On the other hand, such water-soluble compounds as amines and fatty acids have raised a problem that their decomposition activity is considerably lowered with increasing amount of moisture in a gas to be treated or that the coexistence of such a water-soluble compound with a sulfur-type smell causes poisoning of such coexistent gases, which suppresses their respective decomposition activity.
The present invention has been made in view of the foregoing problems associated with catalytic purification performed by a conventional gas-purifying apparatus using a catalyst, particularly by a garbage disposal apparatus, which problems become serious at low temperatures. Accordingly, it is an object of the present invention to provide a purification catalyst and a gas-purifying apparatus which are capable of rapidly removing a smell and harmful substances satisfactorily at relatively low temperatures even if the gas to be purified contains moisture and a great variety of coexistent gas components.